1. Field of the Invention
The present invention is generally directed to an optical device and, more specifically, a planar-type polarization independent optical isolator.
2. Technical Background
Optical isolators have been utilized in a variety of optical systems to reduce reflections that adversely effect the operation of the systems, such as by disrupting the oscillation of a laser and/or interfering with in-line optical amplifiers. Known optical isolators use a wide variety of components to achieve optical isolation. Non-planar, optical isolators, for example, typically utilize birefringent crystal plates (e.g., rutiles), half-wave plates and latching garnets or non-latching garnets with external magnets.
Optical circulators have also been utilized in a variety of optical systems to, for example, couple a bidirectional fiber to both an input fiber and an output fiber. Non-planar optical circulators have also generally utilized birefringent crystal plates (e.g., rutiles), half-wave plates and latching or non-latching garnets with external magnets.
A rutile is a birefringent material that typically divides a light ray into at least two orthogonal rays (i.e., an ordinary ray and an extraordinary ray). When implemented in an optical isolator or an optical circulator, at least one rutile normally functions as a walk-off element, with a first rutile typically splitting an incoming optical signal into ordinary and extraordinary component beams and a last (e.g., a second) rutile normally causing the two separate beams to become coincident and reform the original incoming optical signal. When utilized in optical isolators and optical circulators, a latching garnet non-reciprocally rotates the component beams of an input signal, typically, by forty-five degrees and a half-wave plate is generally used to reciprocally rotate the component beams an additional forty-five degrees.
Due to the recent increase in demand for optical isolators and optical circulators, to be used with dense wavelength division multiplexing (DWDM) systems, reducing the size and cost of optical isolators and optical circulators has become increasingly important. As such, it would be desirable to develop practical planar-type optical devices (e.g., optical isolators and optical circulators) that are fabricated using standard semiconductor manufacturing techniques.
An embodiment of the present invention is directed to a planar-type optical isolator that includes a substrate, a first mode splitter, a second mode splitter and a phase shift region formed on the substrate between the first mode splitter and the second mode splitter. The first mode splitter is formed on the substrate and receives an incident optical signal through an input port and splits the incident optical signal into a first incident mode and a second incident mode. The second mode splitter is formed on the substrate and combines a first rotated incident mode and a second rotated incident mode to reform the incident optical signal at an output port. The second mode splitter receives a reflected optical signal on the output port and splits the reflected optical signal into a first reflected mode and a second reflected mode. The phase shift region is formed on the substrate between the first mode splitter and the second mode splitter and includes a nonreciprocal phase shift section and reciprocal phase shift section. The phase shift region passes the reflected optical signal without altering its modes, while causing the first incident mode to become the second rotated incident mode and the second incident mode to become the first rotated incident mode. The first mode splitter directs the first reflected mode and the second reflected mode away from the input port.
Additional features and advantages of the invention will be set forth in the detailed description which follows and will be apparent to those skilled in the art from the description or recognized by practicing the invention as described in the description which follows together with the claims and appended drawings.
It is to be understood that the foregoing description is exemplary of the invention only and is intended to provide an overview for the understanding of the nature and character of the invention as it is defined by the claims. The accompanying drawings are included to provide a further understanding of the invention and are incorporated and constitute part of this specification. The drawings illustrate various features and embodiments of the invention which, together with their description serve to explain the principals and operation of the invention.